Metadata Visibility Configuration
Applies to: SQL Server Azure SQL Database Azure SQL Managed Instance Azure Synapse Analytics Analytics Platform System (PDW)
The visibility of metadata is limited to securables that a user either owns or on which the user has been granted some permission.
For example, the following query returns a row if the user has been granted a permission such as SELECT or INSERT on the table myTable
.
SELECT name, object_id
FROM sys.tables
WHERE name = N'myTable';
GO
However, if the user does not have any permission on myTable
, the query returns an empty result set.
Metadata visibility configuration only applies to the following securables.
Catalog views
Metadata exposing built-in functions
Compatibility views
Database Engine sp_help stored procedures
Information schema views
Extended properties
Metadata visibility configuration does not apply to the following securables.
Log shipping system tables
Database maintenance plan system tables
Replication system tables
SQL Server Agent system tables
Backup system tables
Replication and SQL Server Agent sp_help stored procedures
Limited metadata accessibility means the following:
Queries on system views might only return a subset of rows, or sometimes an empty result set.
Metadata-emitting, built-in functions such as OBJECTPROPERTYEX may return
NULL
.The Database Engine
sp_help
stored procedures might return only a subset of rows, orNULL
.As a result, applications that assume public metadata access will break.
SQL modules, such as stored procedures and triggers, run under the security context of the caller and, therefore, have limited metadata accessibility. For example, in the following code, when the stored procedure tries to access metadata for the table myTable
on which the caller has no rights, an empty result set is returned. In earlier releases of SQL Server, a row is returned.
CREATE PROCEDURE assumes_caller_can_access_metadata
BEGIN
SELECT name, object_id
FROM sys.objects
WHERE name = N'myTable';
END;
GO
To allow callers to view metadata, you can grant the callers VIEW DEFINITION permission or starting with SQL Server 2022 either VIEW SECUIRITY DEFINITION or VIEW PERFORMANCE DEFINITION at an appropriate scope: object level, database level, or server level. Therefore, in the previous example, if the caller has VIEW DEFINITION permission on myTable
, the stored procedure returns a row. For more information, see GRANT (Transact-SQL) and GRANT Database Permissions (Transact-SQL).
You can also modify the stored procedure so that it executes under the credentials of the owner. When the procedure owner and the table owner are the same owner, ownership chaining applies, and the security context of the procedure owner enables access to the metadata for myTable
. Under this scenario, the following code returns a row of metadata to the caller.
Pastaba
The following example uses the sys.objects catalog view instead of the sys.sysobjects compatibility view.
CREATE PROCEDURE does_not_assume_caller_can_access_metadata
WITH EXECUTE AS OWNER
AS
BEGIN
SELECT name, object_id
FROM sys.objects
WHERE name = N'myTable'
END;
GO
Pastaba
You can use EXECUTE AS to temporarily switch to the security context of the caller. For more information, see EXECUTE AS (Transact-SQL).
Metadata visibility configuration can play an important role in your overall security plan. However, there are cases in which a skilled and determined user can force the disclosure of some metadata. We recommend that you deploy metadata permissions as one of many defenses-in-depth.
It is theoretically possible to force the emission of metadata in error messages by manipulating the order of predicate evaluation in queries. The possibility of such trial-and-error attacks is not specific to SQL Server. It is implied by the associative and commutative transformations permitted in relational algebra. You can mitigate this risk by limiting the information returned in error messages. To further restrict the visibility of metadata in this way, you can start the server with trace flag 3625. This trace flag limits the amount of information shown in error messages. In turn, this helps to prevent forced disclosures. The tradeoff is that error messages will be terse and might be difficult to use for debugging purposes. For more information, see Database Engine Service Startup Options and Trace Flags (Transact-SQL).
The following metadata is not subject to forced disclosure:
The value stored in the
provider_string
column ofsys.servers
. A user that does not have ALTER ANY LINKED SERVER permission will see aNULL
value in this column.Source definition of a user-defined object such as a stored procedure or trigger. The source code is visible only when one of the following is true:
The user has VIEW DEFINITION permission on the object.
The user has not been denied VIEW DEFINITION permission on the object and has CONTROL, ALTER, or TAKE OWNERSHIP permission on the object. All other users will see
NULL
.
The definition columns found in the following catalog views:
sys.all_sql_modules
sys.server_sql_modules
sys.default_constraints
sys.numbered_procedures
sys.sql_modules
sys.check_constraints
sys.computed_columns
The
ctext
column in thesyscomments
compatibility view.The output of the
sp_helptext
procedure.The following columns in the information schema views:
INFORMATION_SCHEMA.CHECK_CONSTRAINTS.CHECK_CLAUSE
INFORMATION_SCHEMA.DOMAINS.DOMAIN_DEFAULT
INFORMATION_SCHEMA.ROUTINES.ROUTINE_DEFINITION
INFORMATION_SCHEMA.COLUMNS.COLUMN_DEFAULT
INFORMATION_SCHEMA.ROUTINE_COLUMNS.COLUMN_DEFAULT
INFORMATION_SCHEMA.VIEWS.VIEW_DEFINITION
OBJECT_DEFINITION() function
The value stored in the password_hash column of
sys.sql_logins
. A user that does not have CONTROL SERVER or starting with SQL Server 2022 the VIEW ANY CRYPTOGRAPHICALLY SECURED DEFINITION permission will see aNULL
value in this column.
Pastaba
The SQL definitions of built-in system procedures and functions are publicly visible through the sys.system_sql_modules
catalog view, the sp_helptext
stored procedure, and the OBJECT_DEFINITION() function.
Pastaba
The system stored procedure sp_helptext
is not supported in Azure Synapse Analytics. Instead, use the sys.sql_modules
object catalog view.
The following are some general principles to consider regarding metadata visibility:
Fixed roles implicit permissions
Scope of permissions
Precedence of DENY
Visibility of subcomponent metadata
Metadata that can be accessed by fixed roles depends upon their corresponding implicit permissions.
Permissions at one scope imply the ability to see metadata at that scope and at all enclosed scopes. For example, SELECT permission on a schema implies that the grantee has SELECT permission on all securables that are contained by that schema. The granting of SELECT permission on a schema therefore enables a user to see the metadata of the schema and also all tables, views, functions, procedures, queues, synonyms, types, and XML schema collections within it. For more information about scopes, see Permissions Hierarchy (Database Engine).
Pastaba
The UNMASK permission does not influence metadata visibility: granting UNMASK alone will not disclose any Metadata. UNMASK will always need to be accompanied by a SELECT permission to have any effect. Example: granting UNMASK on database scope and granting SELECT on an individual Table will have the result that the user can only see the metadata of the individual table from which they can select, not any others.
DENY typically takes precedence over other permissions. For example, if a database user is granted EXECUTE permission on a schema but has been denied EXECUTE permission on a stored procedure in that schema, the user cannot view the metadata for that stored procedure.
Additionally, if a user is denied EXECUTE permission on a schema but has been granted EXECUTE permission on a stored procedure in that schema, the user cannot view the metadata for that stored procedure.
For another example, if a user has been granted and denied EXECUTE permission on a stored procedure, which is possible through your various role memberships, DENY takes precedence and the user cannot view the metadata of the stored procedure.
The visibility of subcomponents, such as indexes, check constraints, and triggers is determined by permissions on the parent. These subcomponents do not have grantable permissions. For example, if a user has been granted some permission on a table, the user can view the metadata for the tables, columns, indexes, check constraints, triggers, and other such subcomponents. Another example is granting SELECT on only an individual column of a given table: this will allow the grantee to view the metadata of the whole table, including all columns. One way to think of it, is that the VIEW DEFINITION permission only works on entity-level (the table in this case) and is not available for Sub-entity lists (such as column or security expressions).
The following code demonstrates this behavior:
CREATE TABLE t1
(
c1 int,
c2 varchar
);
GO
CREATE USER testUser WITHOUT LOGIN;
GO
EXECUTE AS USER='testUser';
SELECT OBJECT_SCHEMA_NAME(object_id), OBJECT_NAME(object_id), name FROM sys.columns;
SELECT * FROM sys.tables
-- this returns no data, as the user has no permissions
REVERT;
GO
-- granting SELECT on only 1 column of the table:
GRANT SELECT ON t1(c1) TO testUser;
GO
EXECUTE AS USER='testUser';
SELECT OBJECT_SCHEMA_NAME(object_id), OBJECT_NAME(object_id), name FROM sys.columns;
SELECT * FROM sys.tables
-- this returns metadata for all columns of the table and thge table itself
REVERT;
GO
DROP TABLE t1
DROP USER testUser
Some metadata must be accessible to all users in a specific database. For example, filegroups do not have conferrable permissions; therefore, a user cannot be granted permission to view the metadata of a filegroup. However, any user that can create a table must be able to access filegroup metadata to use the ON filegroup or TEXTIMAGE_ON filegroup clauses of the CREATE TABLE statement.
The metadata that is returned by the DB_ID() and DB_NAME() functions is visible to all users.
This is a list of the catalog views that are visible to the public role.
sys.partition_functions
sys.partition_schemes
sys.filegroups
sys.database_files
sys.partitions
sys.schemas
sys.sql_dependencies
sys.parameter_type_usages
sys.partition_range_values
sys.data_spaces
sys.destination_data_spaces
sys.allocation_units
sys.messages
sys.configurations
sys.type_assembly_usages
sys.column_type_usages
GRANT (Transact-SQL)
DENY (Transact-SQL)
REVOKE (Transact-SQL)
EXECUTE AS Clause (Transact-SQL)
Catalog Views (Transact-SQL)
Compatibility Views (Transact-SQL)